System design case studies

9 worked system design walkthroughs: requirements, capacity estimates, APIs, data models, deep dives and trade-offs.

• URL Shortener: Turn a long URL into a short code that redirects back to it — the classic first system design interview question.
• Instagram: Design a photo-sharing social network: users post images, follow other users, and see a personalized feed of posts from the people they follow.
• Twitter / X: Design a microblogging platform: users post short messages ('tweets'), follow other users, and see a timeline of tweets from the people they follow.
• WhatsApp: Design a real-time messaging system: one-to-one and group chats with reliable delivery, delivery/read receipts, and end-to-end encryption.
• Uber: Design a ride-hailing system: riders request a trip, nearby drivers get matched to them in real time, and both sides track the trip's location and price live.
• YouTube: Design a video platform where anyone can upload a video and anyone else can watch it instantly, at whatever quality their connection supports.
• Google Drive: Design a cloud file storage and sync service: upload any file, access it from any device, share it with others, and have edits stay consistent even when made offline or from multiple places at once.
• E-commerce Platform: Design an online storefront: browse and search a catalog, hold items in a cart, and check out reliably — without overselling inventory or charging a customer twice.
• Netflix: Design a subscription video-streaming service: a fixed, licensed catalog watched by tens of millions of people simultaneously, on every device, with playback that resumes exactly where you left off.